This invention relates to a static eliminator.
A conventional static eliminator has only a short flying distance of ions. In particular, an alternate current type of static eliminator has a very short flying distance of ions since plus ions and minus ions recombine to each other immediately after their generation. Therefore, the ions must be flied away by a blower. On the other hand, a direct current type of static eliminator can achieve a more flying distance to some extent. However, it merely reaches 70 cm at most. As a result, in actual use, sufficient effects of static elimination cannot be achieved because of lack of flying distance of ions.
As shown in FIGS. 1 through 3, the voltage in alternate current input is boosted to be discharged from discharge electrodes or needles 14, 14 in a static eliminator 10 and the ions thus generated are directed by a fan 70 toward a body 74 to be statically eliminated. In this case, since the distance between the needles 14, 14 are relatively short, the electric field on the electrodes is strengthened. As a result, corona discharge is more likely generated from the discharge needles.
As for one example, FIG. 4 shows a situation in that the area where static electricity cannot be removed exists since the flying distance from the discharge electrode 14 is short and the ions do not reach the center area between the discharge electrodes 14, 14 which are provided on power supply lines 12, 12.
As for another example, FIG. 5 shows another situation in that static electricity is eliminated in a clean room for semiconductor production. Since the ions 20 issued from the static eliminator 10 provided on the ceiling 22 reach 1 meter at most from the ceiling 22, static electricity cannot be eliminated from a person 24, work 26 and the like.
As for a still another example, FIG. 6 shows a still another situation in that the area where static electricity cannot be eliminated exists in the central portion between the static eliminators 10,10 provided in the gate 28 since the ions 20 do not reach. Therefore, the gate should be made narrow which results in inconvenience in actual use.
Thus, with conventional static eliminators, sufficient effects of static elimination cannot be achieved in a large area because of lack of flying distance of ions.
FIG. 16 shows a still another example of static eliminator. In FIG. 16, the static eliminator is of an alternate current type, and alternately issues plus ions 15 in a positive half cycle and minus ions 17 in a next negative half cycle from a discharge electrode 14. Thus, the plus ions 15 and minus ions 17 issued from the discharge electrode 14 are, respectively, drawn back by the minus ions 17 and the plus ions 15 of opposite polarities and recombine them to disappear. Therefore, the static eliminator of this type cannot fly the issued ions away sufficiently.
Then, as shown in FIG. 17, a strong stream of air should be led around the discharge electrode 14 to prevent plus ions 15 and minus ions 17 from recombining to each other. Actually, unless the compressed air is used, or a blower or a fan is used to blow the discharge electrode 14, the generated ions cannot be taken out.
However, this static eliminator has an advantage in that if stream of air is supplied, plus ions 15 and minus ions 17 always come out in the mixed state. Then, the mixing of ions is in a good condition and the distribution balance of ions is also in a good condition.
On the other hand, as shown in FIG. 18, in a direct current type of static eliminator, two discharge electrodes or needles 14a, 14b are separately provided for issuing plus ions 15 and minus ions 17, respectively. Each of discharge needles issues ions of opposite polarity. In other words, the positive needle 14a issues plus ions and the negative needle 14b issues minus ions. Since each of discharge electrodes and the ions issued therefrom are of the same polarity, the ions are flied or pushed away by Coulomb""s force. In other words, the ions 15, 17 automatically flies away to diffuse through a long distance without use of the compressed air, blower or fan. Therefore, its obtained long flying distance is characteristic of the static eliminator of this type.
However, since the distribution of plus ions and minus ions differs in position, the distribution balance of ions is not good. In order to overcome this disadvantage, the polarity of each of the discharge electrodes is caused to reverse sequentially so that the ions are easily mixed as much as possible. However, in this case, since the ions coming later have opposite polarity, the ions first come out are drawn back by the later coming ions, which results in the short flying distance.
Moreover, since the ions of opposite polarities are issued from the two electrodes in the physically separate positions, the mixing of the ions is not attained more than that of one electrode. In other words, plus-tendency ion balance is generated near the plus electrode and minus-tendency ion balance is generated near the minus electrode. When the polarity is reversed and the period for cycle of reversal of polarity is long, the variation in balance of ions appears along time axis. In order to mix the ions completely, the period for cycle of reversal of polarity should be shortened. However, if do so, this static eliminator approaches the alternate current type of static eliminator. In such a case, the ions do not fly away.
Thus, conventional systems have its merits and demerits. There has been no perfect static eliminator which has long flying distance and good balance of ions unless the stream of air by blowers, etc is utilized.
It is therefore an object of the present invention to provide a static eliminator which can extend flying distance of ions and can attain effects of static elimination through wide area sufficiently.
To accomplish the above-mentioned object, there is provided a direct current type of static eliminator which comprises one pair of discharge electrodes, one of said discharge electrode issuing ions while the other discharge electrode issues ions of opposite polarity.
In addition to the foregoing, the polarity of ions issued from each of the opposed discharge electrodes is caused to switch over to the opposite polarity. At that time, it is preferred that the switchover for each of discharge electrodes is made in timed relationship.
It is another object of the present invention to provide a static eliminator which can extend flying distance of ions without blowing of the discharge electrode by use of compressed air, blower or fan, suppress the variation in balance of ions in position, and suppress the variation in balance of ions along time axis.
To accomplish the above-mentioned object, there is provided a static eliminator which has a rotary ionizer or rotary ion issuing discharge electrodes.
It is a still another object of the present invention to provide an array type of static eliminator which can attain a more wide static eliminating space.
To accomplish the above-mentioned object, there is provided an array type of static eliminator in which more than three discharge electrodes are disposed and ions issued from adjacent discharge electrodes are of an opposite polarity.